You may also want to check out the Eisenberg’s book A Call to Action which is also about web marketing conversion rates.

My main point is that driving traffice to your site through PPC or regular search engine marketing doesn’t add a ton of value if you don’t CONVERT that traffic. While at a high level the web marketing fundamentals article definitely stands, at an incremental improvement level you can’t beat the detailed analysis of a conversion rate specialist (or become one!).